pragma once replaced

added constexpr

P0959.md

@@ -105,6 +105,7 @@ P0959R2 was discussed by LEWGI in Kona with the following feedback:
 Based on this feedback and further considerations, the following changes have been done in this version:
 * Added detailed explanation of the algorithms for generating uuids.
 * `from_string()` and non-member `swap()` declared with `noexcept`.
+* `from_string()` and `is_valid_uuid()` declared with `constexpr`.
 * The `uuid` type is now defined as a class.
 * Added an exposition-only member to hint and the possible internal representation of the uuid data.
 * Added `uuid` constructors from arrays.
@@ -506,21 +507,11 @@ namespace std {
 
       constexpr std::strong_ordering operator<=>(uuid const&) const noexcept = default;
      
-      template<class CharT = char>
+      template<typename StringType>
-      static bool is_valid_uuid(CharT const * str) noexcept;
+      constexpr static bool is_valid_uuid(StringType const & str) noexcept;
-     
+         
-      template<class CharT = char,
+      template<typename StringType>
-               class Traits = std::char_traits<CharT>,
+      constexpr static uuid from_string(StringType const & str) noexcept;   
-               class Allocator = std::allocator<CharT>>
-      static bool is_valid_uuid(std::basic_string<CharT, Traits, Allocator> const & str) noexcept;
-     
-      template<class CharT = char>
-      static uuid from_string(CharT const * str) noexcept;
-   
-      template<class CharT = char, 
-               class Traits = std::char_traits<CharT>,
-               class Allocator = std::allocator<CharT>>
-      static uuid from_string(std::basic_string<CharT, Traits, Allocator> const & str) noexcept;
    private:
       template <class Elem, class Traits>
       friend std::basic_ostream<Elem, Traits> & operator<<(std::basic_ostream<Elem, Traits> &s, uuid const & id);     
@@ -598,13 +589,8 @@ namespace std {
    public:
      explicit uuid_name_generator(uuid const& namespace_uuid) noexcept;
      
-     template<class CharT = char>
+     template<typename StringType>
-     uuid operator()(CharT const * name);
+     uuid operator()(StringType const & name);
-     
-     template<class CharT = char,
-              class Traits = std::char_traits<CharT>,
-              class Allocator = std::allocator<CharT>>
-     uuid operator()(std::basic_string<CharT, Traits, Allocator> const & name);
    };
 }
 ```
@@ -714,21 +700,11 @@ namespace std {
 
       constexpr std::span<std::byte const, 16> as_bytes() const;
      
-      template<class CharT = char>
+      template<typename StringType>
-      static bool is_valid_uuid(CharT const * str) noexcept;
+      constexpr static bool is_valid_uuid(StringType const & str) noexcept;
-     
+         
-      template<class CharT = char,
+      template<typename StringType>
-               class Traits = std::char_traits<CharT>,
+      constexpr static uuid from_string(StringType const & str) noexcept;  
-               class Allocator = std::allocator<CharT>>
-      static bool is_valid_uuid(std::basic_string<CharT, Traits, Allocator> const & str) noexcept;
-     
-      template<class CharT = char>
-      static uuid from_string(CharT const * str) noexcept;
-   
-      template<class CharT = char, 
-               class Traits = std::char_traits<CharT>,
-               class Allocator = std::allocator<CharT>>
-      static uuid from_string(std::basic_string<CharT, Traits, Allocator> const & str) noexcept;
    private:
       template <class Elem, class Traits>
       friend std::basic_ostream<Elem, Traits> & operator<<(std::basic_ostream<Elem, Traits> &s, uuid const & id);     
@@ -841,6 +817,12 @@ auto id1 = uuid::from_string<char, std::char_traits<char>>(
 std::string str{ "47183823-2574-4bfd-b411-99ed177d3e43" };
 auto id2 = uuid::from_string<char, std::char_traits<char>>(str);      // [2]
 ```
+However, to simplify the definition, these two overloads have been replaced with a single one:
+```
+template <typename StringType>
+constexpr static std::optional<uuid> from_string(StringType const & str);
+```
+The `is_valid_uuid()` function and the `uuid_name_generator`'s call operator are now defined in the same manner. 
 
 #### Need more explanations about the choices of ordering and how the RFC works in that regard.
 

include/uuid.h

@@ -1,4 +1,5 @@
-#pragma once
+#ifndef STDUUID_H
+#define STDUUID_H
 
 #include <cstring>
 #include <string>
@@ -62,7 +63,7 @@ namespace uuids
    namespace detail
    {
       template <typename TChar>
-      constexpr inline unsigned char hex2char(TChar const ch)
+      constexpr inline unsigned char hex2char(TChar const ch) noexcept
       {
          if (ch >= static_cast<TChar>('0') && ch <= static_cast<TChar>('9'))
             return static_cast<unsigned char>(ch - static_cast<TChar>('0'));
@@ -74,7 +75,7 @@ namespace uuids
       }
 
       template <typename TChar>
-      constexpr inline bool is_hex(TChar const ch)
+      constexpr inline bool is_hex(TChar const ch) noexcept
       {
          return
             (ch >= static_cast<TChar>('0') && ch <= static_cast<TChar>('9')) ||
@@ -83,17 +84,15 @@ namespace uuids
       }
 
       template <typename TChar>
-      constexpr std::basic_string_view<TChar> to_string_view(TChar const * str)
+      constexpr std::basic_string_view<TChar> to_string_view(TChar const * str) noexcept
       {
          if (str) return str;
          return {};
       }
 
       template <typename StringType>
-      constexpr std::basic_string_view<
+      constexpr std::basic_string_view<typename StringType::value_type, typename StringType::traits_type>
-         typename StringType::value_type,
+      to_string_view(StringType const & str) noexcept
-         typename StringType::traits_type>
-      to_string_view(StringType const & str)
       {
          return str;
       }
@@ -947,3 +946,5 @@ namespace std
       }
    };
 }
+
+#endif /* STDUUID_H */